Molecular Engineering of Solid-State Packing For Wide Area Printed Electronics: Understanding Exciton Delocalization and Free Carrier Generation
Abstract
Organic photovoltaics (OPVs) have the unique potential to serve as low-cost power sources in DoD missions ranging from high-endurance UAVs to portable power in the field. This potential arises from their unrivalled power/weight ratios, and their ability to form inherently flexible, conformal, and heavy-metal free thin films that can enable novel geometries and form factors. OPV efficiencies have continued to soar in recent years following the introduction of new families of non-fullerene acceptors, and now exceed 19%. Nevertheless, the voltage deficit - the difference between the experimental open-circuit voltage (VOC) and the theoretical VOC based onthe bandgap # must be reduced to approach fundamental efficiency limits. A key barrier in this regard is the large donor-acceptor energetic offset required to overcome the exciton binding energy (Eb) and produce free charge in many systems. Recently, evidence hasbeen accumulating that Eb in certain donors and acceptors is low, presenting the possibility for minimal energetic offsets in next-generation OPVs. In this proposal, we address this issue by combining molecular synthesis with photophysical studies, building on preliminary data that point to complementary strategies of molecular design, and morphology control, in order to maximize free chargegeneration in neat donors and acceptors for high performance OPVs. The specific objectives of the proposal are as follows: 1) We will synthesize new generations of luminescent NFAs and donors designed to facilitate exciton separation in the solid state by (i) modulation of intramolecular charge transfer character of NFAs and donors, (ii) systematic variation of conjugation motifs and shapes of NFAs, and (iii) careful control of exciton delocalization and charge transfer in the crystalline aggregates of NFAs self-assembled by clearly defined supramolecular interactions between the species. 2) We will study the structure-property relationships betweensolid-state packingof the species and free charge generation mechanisms in the films. We will correlate different structural parameters of NFAs and donors with exciton delocalization, exciton binding energies, and measure kinetics of charge generation, transport,and recombination to understand how free charge generation occurs in neat acceptors and donors to improve blend efficiency. 3) We will elucidate the role of the third component in ternary OPVs (TOPVs) in improving device photovoltaic efficiencies. Specifically, we will investigate the role of third components modulating the intermolecular interactions between the species in solutions and films of NFAs and donors, affecting the electronic landscape, molecular packing, morphology, electron-phonon coupling, and ultimately the performance of TOPVs, leveraging and supporting the studies of solid-state packing, molecular design, and photophysics, proposed in objectives 1 and 2. Approved for Public Release.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 08, 2024
- Source ID
- N000142412103
Entities
People
- David Ginger
Organizations
- Office of Naval Research
- United States Navy
- University of Washington